This proposal is directed toward measuring the lateral mobility of various cell surface components. This will be accomplished by labeling the cell with fluorescent molecules specific for the cell surface and measuring the fluorescence recovery after photobleaching in local regions of the cell surface of single, living cells. The new technique of digitized video microscopy will be used to trace the time evolution of the labeled components as the cell responds to various stimuli. A major objective is to explore which elements of the cytoskeleton or the glycocalyx peripheral to the plasma membrane determine the rates of membrane glycoprotein lateral diffusion. These studies will focus on a selected set of murine fibroblast plasma membrane antigens defined by monoclonal antibodies. After determining whether the antibody label affects the antigen diffusion rate, a correlation of lateral diffusion rates with local cytoskeletal and glycocalyx structure will be conducted. Further, a series of perturbations of the cytoskeletal and the extracellular matrix structure will be performed to identify those elements of the peripheral structure which can interact with and alter the mobility of given plasma membrane components. A longer range objective is to explore whether and under what conditions cell surface proteins are mobile in solid tissues. To accomplish this aim, our studies will be adapted to epithelial cell cultures exhibiting basal lamina and cell-cell contact interactions, in order that the influence of these interactions on lateral mobility may be ascertained. It is hoped that these approaches can be extended to study changes in cell surface dynamics accompanying the ability of cancer cells to invade and penetrate the basal lamina during steps in the metastatic process.